MATTAWAMKEAG, Maine — A firefighter looking out a side door of the fire station saw the fire that eventually destroyed a 2½ -story house, leaving several family members homeless on Thursday. Two firefighters and a resident were treated for heat exhaustion, officials said.

The house at 11 Depot St. is within 200 yards of the station, but a combination of the home’s age and the fact that no one was home to notice the flames doomed the house, officials said.

“The fire started in the rear of the building. We haven’t been able to pinpoint exactly where,” Mattawamkeag Fire Chief Robert Powers said Thursday. “They did have several animals in the house” that died.

The fire was so far along when firefighters called 911 about 1:45 p.m. that they couldn’t save the house.

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The flames already had burned up a rear wall into the ceiling and attic area, said Powers, who believed the house was built in the 1800s.

Powers was pleased that firefighters saved a house about 10 feet away.

Next-door neighbor Violet Pettengill said three generations of the Norris family lived at the house but that no one was home. Homeowner Richard Norris’ wife, Robin, had taken her daughter to a doctor’s appointment in Bangor, Pettengill said.

“The first thing I heard was this loud ‘pop’ and then I heard all the firetrucks,” Pettengill said.

Norris said he was at work when he got the call about the fire. His wife’s first awareness of it came when she turned onto Depot Street in her car and saw firetrucks. She got out of her vehicle, approached other family members and burst into tears as they consoled her.

Firefighters from East Millinocket, Lee, Lincoln and Medway assisted town firefighters in dousing the flames and shuttling water to the scene with a tanker truck.

The fire wasn’t reported under control until about 5:25 p.m.

Powers said that he expected firefighters would have to stay on scene another two or three hours. They might also have to return to douse flare-ups, he said.

The cause of the fire is unknown. The state fire marshal’s office will investigate, Powers said.